As a method for imparting water/oil repellency to a surface of an article (such as a fiber product, etc.), a method of treating the article by using a water/oil repellent composition having dispersed in a liquid medium a copolymer having structural units based on a monomer having a polyfluoroalkyl group, is known. The article treated by using the water/oil repellent composition is required to have such a property (heavy-rain durability) that the water/oil repellency is not lowered substantially even when exposed to heavy rainfall conditions.
As a water/oil repellent composition excellent in heavy-rain durability, for example, the following water/oil repellent composition has been proposed.
A water/oil repellent composition containing a copolymer having structural units based on following monomer (1) and structural units based on the following monomer (2), wherein the proportion of the structural units based on the monomer (2) is from 30 to 80 mol % in the total (100 mol %) of the structural units based on the monomer (1) and the structural units based on the monomer (2) (Patent Document 1).
Monomer (1): a (meth)acrylate having a C1-6 perfluoroalkyl group, etc.
Monomer (2): a (meth)acrylate having a C20-30 alkyl group.